1. Field of the Invention
The present invention relates to a gas turbine engine, and more particularly to a shroud tip ring that forms a blade outer air seal with a blade tip of the engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a row of rotating blades. These rotating blades define a space between a blade tip and an inner shroud of the casing. This space or gap allows for the gas or air in the turbine engine to flow around or bypass the blades such that no work is extracted. It is desirable to minimize this gas to prevent as much airflow bypass as possible without rubbing the blade tips against the inner-casing surface.
During startup or transient operation of the turbine engine, the gap between the shroud and the blade tip can be greater than a gap when the engine is operating under normal load. During startup, the gap should be large to allow for thermal expansion of the blade and rotor in order to prevent rubbing of the blade tip. This occurs because the blades tend to grow thermally faster than the outer shrouds and casing. Thus, during engine warm-up to steady state operating conditions, the blade tip could grow such that the tip would rub and reduce excessively and produce a permanent gap of large spacing. When normal operating conditions are met, the gap should be as narrow as possible to improve performance. When normal operating conditions are met, the shaft drive members are moved to the extended position such that the ring segments are moved inward to make the gap the smallest of the two positions.
Prior art outer shrouds use a plurality of shroud segments forming an annular ring around the blades. There are generally eight or more of these segments, and each includes a separate motor or drive device to move the respective segment in the radial direction to control the gap between the blade tip and the inner surface of the segment. The more shroud segments that are used, the more gaps between adjacent segments exist. The more gaps that exist, the more leakage occurs across the gaps.
Thus, it is an objective of the present invention to reduce the number of gaps in shroud segments used in a gas turbine engine, and to minimize the gap between the rotary blade tips and the shroud segments in order to reduce the bypass of the gas stream at the blade tip and shroud segment.
Another objective is to simplify the complexity of the shroud segment assembly and drive motor means, and to provide a more even gap along the complete circumference of the shroud ring assembly.